Pyrazolecarboxamide derivatives having a carbamoyl group at the 3-position are useful compounds as, e.g., a dye intermediate and a base compound for producing medicines or agricultural chemicals, and are especially useful as an intermediate for photographic dyes (see, e.g., JP-A-51-77327 and JP-A-63-139949). (The term "JP-A" as used herein means an "unexamined published Japanese patent application.")
Several processes for synthesizing pyrazolecarboxamide derivatives have conventionally been known; these processes are generally based on the aminolysis of esters (see, e.g., JP-A-63-139949). However, when a secondary amine or arylamine having reduced nucleophilicity, such as morpholine or aniline, is used, the aminolysis reaction should be conducted at a high temperature for a prolonged time period, although aminolysis with a highly nucleophilic primary alkylamine, such as ethanolamine, proceeds relatively easily. Thus, those prior art processes are unsuitable for industrial production.
On the other hand, there are also several known processes for synthesizing pyrazolecarboxamide derivatives without via ester aminolysis. Such processes, for example, include a method in which a 3-carboxylated compound is reacted with a sulfonic acid chloride derivative to yield a mixed acid anhydride and the anhydride is amidated (see JP-A-58-111641) and a method in which amidation is conducted after the 5-position hydroxyl group is protected by being converted to an ester group (see JP-A-2-193973 and JP-A-2-193974). However, the former method, in which the desired compound is obtained via a mixed acid anhydride, has a drawback that when the starting compounds have a reactive hydroxyl group in the molecule, side reactions occur in a considerable degree to result in a reduced yield. The latter method, which involves protection of a hydroxyl group, has a drawback that the necessity of additional two steps, i.e., protection and protecting-group elimination, leads to an increased cost, although a high yield is attainable.
There is a method in which a Lewis acid is used for amidating an ester by aminolysis. This method, however, is not frequently used generally, since the acidity of the Lewis acid is reduced, or the Lewis acid reacts with an amine to consume the amine. The following are examples of a limited number of such methods.
1. R. D. Gless, Jr., Synth. Comm., 16, 633 (1986)
Aminolysis of a 2-chloropropionic ester PA1 Aminolysis of ethyl acetate or propionate with a primary amine PA1 Aminolysis using an alkylaluminum
2. F. Porta, M. Pizzotti, C. Crotti and S. Cenini, Gazz. Chem. Ital., 118, 475 (1988)
3. J. I. Levin, E. Turos and S. M. Weinreb, Synth. Comm., 12, 989 (1982)
However, methods 1 and 2 have a drawback that the usable substrates are limited to only a small part of aliphatic esters and amines. Method 3 has a drawback that trimethylaluminum used therein as a reagent is an ignitable water-prohibiting compound, although the method is applied to various esters. Thus, these three methods each has a drawback when used for industrial production. In particular, there has been no report on application to a compound having in the molecule a reactive hydroxyl group and a heterocyclic group capable of coordinating with a Lewis acid, such as the substrate compound used in the present invention.
The present inventors made investigations in order to develop a method for synthesizing the desired pyrazolecarboxamide derivative by aminolysis of a pyrazolecarboxylic ester. As a result, it has been found that when a Lewis acid is used as an activating agent, the aminolysis of a pyrazolecarboxylic ester with an amine compound proceeds readily to yield the desired pyrazolecarboxamide derivative. The present inventors have further found that the Lewis acid used for activation functions as a catalyst. In industrial production, this function of the Lewis acid is of great significance from the standpoints of post-treatment after reaction, withdrawal of the reaction product, and environmental conservation.